Containers such as clear or translucent glass bottles are manufactured and filled in an in-line process, and thereafter are capped or sealed to enclose and protect the contents thereof. In this process, it is important that the finish surface or sealing surface of the container be free of defects which would affect proper sealing of the container or cause other problems. Other dimensional characteristics of the container must also be consistent with the sealing device such as a cap or lid, as well as the filling and capping equipment used in the in-line process. The problems associated with an improper container sealing surface or other dimensional flaws should be apparent, such as leaking of the container after the automated filling and capping process, which could include leakage of the liquid contents and/or any gas such as from carbonated liquids. Errors in finish or container dimensions may also result in damage to the filling and capping equipment, or can result in breakage of the container itself or improper operation of the filling and capping process.
An ideal container has a flat (planar) sealing or finish surface. A dip or saddle is an irregularity in the sealing surface which may prevent the container from sealing properly when a cap or lid is applied. A dip is a single localized depression or anomaly in the sealing surface, while a saddle is a saddle-shaped, or more global undulation of the sealing surface. Containers which have dip or saddle defects beyond a certain degree of severity must be rejected to avoid the above problems.
Similarly, an ideal container has a level (horizontal) sealing or finish surface. An out-of-level (tilted) sealing surface may prevent the container from sealing properly when a cap or lid is applied. Containers which are too far out-of-level must also be rejected.
The ideal container also has a smooth circular opening (bore) with a characteristic diameter. A plug (or choked neck) flaw is an irregularity in the bore or a bore having an incorrect diameter, typically a localized or global narrowing of the bore. A plugged bore can cause problems when a glass container is filled, since the filling tube which is inserted into the container may collide with the plug and break the bottle. Or, if the bore diameter is incorrect, a cork or other closing device (such as in a wine bottle) may not fit properly. Containers with opening diameters which are too small or too large, or with bores which are too non-circular, must be rejected.
All containers of the same type should have the same height (i.e., distance from the container base to its sealing surface). Containers which are too tall or too short must be rejected, as they may not be compatible with the filling or sealing equipment. Those defects (dip-saddle, out-of-level, plug and incorrect height) commonly arise during the molding process in the manufacture of glass or other containers. Mechanical inspection systems to detect these flaws have been developed and used in the glass container manufacturing industry with limited success. Further, known inspection systems generally do not provide for inspection of each of the various defects which can occur.
A known dip-saddle inspection system operates by pressing a gasketed nozzle against the container sealing surface and pressurizing the container with air. If the container has any dip or saddle defects, then the gasket does not completely seal the sealing surface and the pressurized air leaks out. The inspection system detects the reduced pressure due to leakage and rejects containers with excessive leakage.
Out-of-level inspection has also been performed by the same mechanical assembly which performs dip-saddle inspection. The gasketed nozzle which is pressed against the container sealing surface is configured so that it can swivel slightly, to conform to an out-of-level sealing surface. However, the nozzle can only swivel through a small angle .theta. from horizontal (two or three degrees, typically). Sealing surfaces which are more out-of-level than .theta. will not seal against the gasket and will fail the pressure test.
Plug inspection has been performed by inserting a cylindrical rod (plunger) into the bore of each container. The diameter of the plunger is chosen to be as large as the largest fill tube which will be used during the filling operation of the given container. If the container is plugged the plunger collides with the plug and resists complete insertion into the bore. This resistance is detected by the inspection system, so that plugged containers can be rejected.
Container height inspection has been performed by the same mechanical assembly which performs plug inspection. A "shoulder" is added to the plunger at an appropriate position and the plunger is driven down until it is stopped by the resistance of the shoulder against the container sealing surface. Adjustable limit switches are coordinated with the plunger assembly so as to identify containers which are too tall or too short.
The primary disadvantage of these mechanical inspection systems is that they are slow. The containers are typically moving down a conveyor during the inspection process, and it is mechanically complex to press a gasketed nozzle against each container sealing surface as it moves along the conveyor and as a separate step insert a plunger into the moving containers. Typical mechanical inspection systems (such as the Emhart Powers Dual Head Gager) have a throughput limit of about 200 containers per minute, while container manufacturers would prefer to sustain rates of 800 containers per minute or more.
Another disadvantage of mechanical plug gaging is that the plunger will sometimes collide with and dislodge a small glass fragment protruding from the container bore wall (called stuck glass), and this fragment will fall to the bottom of the container and stay there. If the stuck glass is fragile it may not cause sufficient resistance to the plunger to trigger rejection of the container. The presence of glass fragments at the bottom of food or beverage containers is of obvious concern. It would be desirable to provide an inspection system which not only would alleviate this problem but also would detect the presence of stuck glass.
Another disadvantage of mechanical dip-saddle gaging is that the pressure leakage technique cannot distinguish between dip and saddle defects. The leakage area of a deep narrow dip may be identical to that of a shallow saddle, so the mechanical gager sees them as identical defects. From the standpoint of manufacturing the containers, however, it is desirable to be able to distinguish these two types of defects. A dip may be harder to seal with a cap or lid than a saddle, so that the manufacturer may wish to accept saddles while rejecting dips. Additionally, the production process errors which produce dips may be different than those which produce saddles, so that distinguishing between dips and saddles may be useful for process monitoring and control.
To potentially avoid various of the problems associated with the mechanical inspection systems, there have been attempts at optical inspection techniques for certain of the container defects desired to be rejected. Such techniques have not been entirely successful as only certain of the defects desired to be found can be detected by the systems. Known optical techniques for dip-saddle gaging typically require continuous and complete rotation of the container to acquire data for the entire container sealing surface as an example, which may even be slower than the mechanical systems and are therefore ineffective. There remains the need for a container inspection system which allows a great deal of flexibility in detecting various flaws or defects in containers reliably, and as an in-line process which allows desired operating speeds to be achieved.